Folded camera structure with an extended light-folding-element scanning range

ABSTRACT

Voice coil motor (VCM) actuators for rotating an optical path folding element (OPFE) over an extended scanning range relative to a scanning/rotation range needed for optical image stabilization (OIS).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of international application PCT/IB2017/057706 filed Dec. 6, 2017, and is related to and claims priority from U.S. Provisional Patent Application No. 62/439,518 filed Dec. 28, 2016, which is incorporated herein by reference in its entirety.

FIELD

Embodiments disclosed herein relate in general to digital cameras and in particular to thin multi-aperture zoom digital cameras.

BACKGROUND

Personal electronic devices such as smartphones having two back cameras (also referred to as “dual-cameras” or “dual-aperture cameras”) are known and available commercially. The two back cameras have respective lenses with different fixed focal lengths and respective image sensors (or simply “sensors”) operated to capture image data (or “image”). Even though each lens/sensor combination is aligned to look in the same direction, each will capture an image of the same scene with a different field of view (FOV).

A Tele camera with adjustable FOV_(T) for maximizing zooming capabilities is disclosed for example in commonly owned and invented PCT patent application PCT/IB2016/057366 titled “Dual-aperture zoom digital camera with automatic adjustable tele field of view”. The adjustable FOV involves scanning enabled by a step motor. Recently, step motors have been replaced by voice coil motor (VCM) technology. VCM actuation is used for autofocus (AF) and\or optical image stabilization (OIS). However, known VCM actuator technology, in particular as used in folded cameras, may have a limited scanning range and a given VCM actuator may perform only OIS, which requires motion compensation in a very limited range.

Systems that rotate an OPFE for OIS are described for example in co-assigned international patent application PCT/IB2016/052179, titled “Auto focus and optical image stabilization in a compact folded camera”.

Therefore, there is a need for, and it would be advantageous to have a VCM actuation mechanism for adjustable FOV_(T) with extended scanning range. In addition, it would be advantageous to have a VCM actuation mechanism for adjustable FOV_(T) with extended scanning range that can simultaneously support scanning in an extended range and OIS.

SUMMARY

Embodiments disclosed herein relate to VCM actuators for Tele folded cameras with adjustable FOV_(T), such as the camera described in PCT/IB2016/057366. The disclosed actuators are designed to maximize zooming and scanning capabilities. Some exemplary disclosed embodiments also allow OIS in parallel with image scanning.

In an exemplary embodiment, there is provided an actuator for rotating an OPFE over a scanning range in which OPFE position is controlled by a non-accurate position sensing mechanism that determines an allowable jitter limit, the actuator comprising: an actuated sub-assembly rigidly coupled to the OPFE and having two hinges that define a rotation axis, and a stationary sub-assembly having two housings, wherein each housing is nested in a respective hinge of the stationary sub-assembly to form a housing-hinge pair, wherein a center-of-mass of the actuated sub-assembly is positioned to coincide with the rotation axis to limit jitter arising from the OPFE being rotated to and stopped at a given OPFE position to be no larger than an allowable limit.

In an embodiment, each housing-hinge pair has a degree of friction designed to assist in limiting the jitter arising from the OPFE being rotated to and stopped at a given OPFE position to be no larger than the allowable limit.

In an embodiment, the stationary sub-assembly includes a position sensor for sensing the given OPFE position.

In an embodiment, the position sensor includes a Hall bar sensing element.

In an embodiment, the scanning range is larger than ±1.5 degrees around a rest position of the OPFE.

In an embodiment, the scanning range is at least ±5 degrees around the rest position of the OPFE.

In an embodiment, the scanning range is up to ±20 degrees around the rest position of the OPFE.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of embodiments disclosed herein are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein, and should not be considered limiting in any way.

FIG. 1A shows an actuator capable of extended scan in an isomeric view according to an exemplary embodiment;

FIG. 1B shows the actuator of FIG. 1A in a backside view;

FIG. 1C shows the actuator of FIG. 1A in an exploded view;

FIG. 2 shows the actuator of FIGS. 1A-C in a folded camera with lens and sensor;

FIG. 3 shows the folded camera and actuator of FIG. 2 in a dual-camera;

FIG. 4 shows a simulation of the effect of a magnetic field in the X direction on a sensing element as function of actuated sub-assembly 116 and magnet 110) rotating around axis 104;

FIG. 5 shows schematically a sensing circuit for the actuator of FIGS. 1A-C;

FIG. 6A shows an actuator capable of extended scan+OIS in an isomeric view according to another exemplary embodiment;

FIG. 6B shows the actuator of FIG. 6 in an exploded view;

FIG. 7 shows the actuator of FIGS. 6A-C in a folded camera with lens and sensor;

FIG. 8 shows the folded camera and actuator of FIG. 7 in a dual-camera;

FIG. 9 shows schematically a sensing circuit for the actuator of FIGS. 6A-C.

DETAILED DESCRIPTION

FIGS. 1A-D illustrate in various views an actuator 100 of a rotational voice coil motor (VCM), according to an example of the presently disclosed subject matter. Actuator 100 enables an extended OPFE scanning range relative to the needs of other systems that rotate an OPFE for OIS (where the rotation is typically of ±1 degree, as e.g. the system described in co-assigned PCT patent application PCT/IB2016/052179) and enables as well adjustment of FOV_(T). FIG. 1A shows actuator 100 in an isometric view, FIG. 1B shows actuator 100 from a back view, and FIG. 1C shows actuator 100 in an exploded view. Actuator 100 enables rotation (in an angle referred to as “φ”) of an OPFE 102 (for example a prism or mirror) around a single axis 104 (i.e. around for example the X axis in the coordinate system shown and used in all figures), as described below. Axis 104 may also be referred to as “rotation axis”. In various embodiments, the extended range of φ may be for example in the range of 10 degrees to 40 degrees (or ±5 degrees to ±20 degrees around an initial “rest” position). In an exemplary embodiment, φ=20 degrees or ±10 degrees around the rest position In comparison, known designs in which the OPFE is rotated (tilted) for OIS purposes only enable a limited rotation range of 0.5 to 3 degrees or ±0.25 to ±1.5 degrees around the rest position.

In actuator 100, OPFE 102 is held in an optical element holder (or simply “holder”) 106, which may be made, for example by plastic molding, fit to the shape of OPFE 102. An actuation magnet 108 is fixedly attached (e.g. glued) to optical element holder 106 from below (negative Z direction in FIG. 1B). A sensing magnet 110 is fixedly attached (e.g. glued) to holder 106 on one side of the holder in a groove 112. Two hinges 114 a and 114 b are fixedly attached (e.g. glued) to holder 106 on two sides. Hinges 114 a and 114 b are made for example of a hard metal, e.g. stainless steel. The assembly of OPFE 102, optical element holder 106, actuation magnet 108, sensing magnet 110, and hinges 114 a and 114 b will be referred to henceforth as “actuated sub-assembly” 116.

Actuator 100 further includes a base 118, made for example of plastic, and two housings 120 a and 120 b also made for example of plastic, housings 120 a and 120 b fixedly attached (e.g. glued) to base 118. Is some embodiments, base 118 and either one or both of housings 120 a and 120 b may be molded as a single part. In some embodiments, housing 120 a and\or housing 120 b may include several parts which are assembled and e.g. glued only during the actuator assembly process. Base 118 and housings 120 a and 120 b form a “stationary sub-assembly” 122. Stationary sub-assembly 122 further includes a Hall bar sensing element 126 and a coil 124, both described below.

Actuated sub-assembly 116 is positioned inside stationary sub-assembly 122 such that hinges 114 a and 114 b are positioned inside housings 120 a and 120 b respectively. Hinges 114 a and 114 b are concentric and lie on axis 104 (parallel to the X axis in the figures). The mechanical structure described allows the rotation of actuated sub-assembly 116 and of OPFE 102 around axis 104. The plastic moldings of base 118 and/or optical element holder 106 may be used as a mechanical stopper for actuated sub-assembly 116 to prevent motion beyond φ degrees.

In some embodiments, axis 104 is positioned through the center-of-mass of actuated sub-assembly 116. The “mass” includes elements 102,106, 108, 110, 114 a and 114 b. In such embodiments, an external rotation of actuator 100 (caused e.g. by a user rotating a device including the actuator) will not cause a relative rotation between actuated sub-assembly 116 and stationary sub-assembly 122.

Actuator 100 further includes a wound coil 124, for example of a stadium shape, typically with a few tens of windings (e.g. in a not limiting range of 50-250) and with a typical resistance of 10-30 ohm. Coil 124 is located below magnet 108 such that nominally their centers overlap when the actuated sub-assembly is at rest. Magnet 108 can be for example a permanent magnet, made from a neodymium alloy (e.g. Nd₂Fe₁₄B) or a samarium-cobalt alloy (e.g. SmCo₅). Magnet 108 can be fabricated (e.g. sintered) such that it changes the magnetic poles direction: on the positive Y side, the North magnetic pole faces the negative Z direction, while on the negative Y side, the North magnetic pole faces the positive Z direction. Coil 124 is connected to external current driving circuit (not shown), the driving circuit capable of sending input currents to coil 124. Current in coil 124 creates a Lorentz force due to the magnetic field of magnet 108: for example, a current in a clockwise direction will create a force in the positive Y direction, while a current in counterclockwise direction will create a force in the negative Y direction. The full magnetic scheme (i.e. the full magnetic simulation of the magnetic field caused by magnet 108) is known in the art, and described, for example, in detail in patent application PCT/IB2016/052179.

When the magnetic force applied by coil 124 is in the positive and negative Y directions, the hinge mechanical structure confines actuated sub-assembly 116 to rotate around axis 104. A Hall bar element 126 can sense the intensity and direction of the magnetic field of sensing magnet 110. Sensing magnet 110 can be for example a permanent magnet, made from a neodymium alloy (e.g. Nd₂Fe₁₄B) or a samarium-cobalt alloy (e.g. SmCo₅). Magnet 110 can be fabricated (e.g. sintered), such that its North pole is to the Z direction when actuator 100 is at rest. Upon actuation, the relative position of actuated sub-assembly 116 and Hall bar element 126 is changed. The intensity and direction of the magnetic field senses by Hall bar element 126 changes as well, and thus the position of actuated sub-assembly 116 can be determined. A closed loop control circuit (not shown) is used to control the position of the actuated sub-assembly and set to the position required by optical demands. The closed loop control circuit has a single input—the signal of Hall bar element 126, and a single output—the amount of current applied in coil 124. The closed loop control circuit may be implemented in an integrated circuit (IC) (not shown). Operation of a closed loop control system with single input and single output (SISO) system is known in the art. Such a closed loop control circuit may, for example, be a linear “proportional-integral-differential” (PID) control. In some embodiments, the single IC may be implemented in a controller inside Hall bar element 126. In other embodiments, the IC may be a separate chip, which can be located externally to the camera.

The step resolution and jitter (noise) of actuator 100, as described below, may be limited by a “non-accurate” sensing mechanism circuitry to 1/1000 of φ. For usage requirements, a 1/80 of φ step resolution may be acceptable, as described in PCT patent application PCT/IB2016/057366. However, after actuator 100 has positioned the OPFE in a specific position, considerations of prevention of image blur require a jitter of no more than 1/200 degree. In system 100 and for example, 1/200 degree is equal to 1/4000 of φ, which is smaller than the 1/1000 φ jitter limit allowed by the sensing circuitry. To address this problem, a friction-based mechanism is provided to limit jitter to a level that does not exceed the allowable limit ( 1/200 degree, which in the example is 1/4000 of φ). For example, in some cases, significant friction may be designed and introduced between hinges 114 a and 114 b and housings 120 a and 120 b. After a control command moves (through a driving current, see below) actuated sub-assembly 116 to a desired position, as required by optical demands and as sensed by a sensing mechanism described below, the driving current may be turned off to reduce jitter caused by a non-accurate sensing mechanism. The significant friction and the positioning of axis 104 through the center-of-mass of actuated sub-assembly 116 will ensure that external torques and forces (caused for example by user hand shake) will maintain actuated sub-assembly 116 fixed relative to stationary sub-assembly 122. The power turn-off also helps reduce the system power consumption.

For example, assume actuated sub-assembly with a mass of 500 mg and a moment of inertia around axis 104 of 1000 mg-mm². Assume a friction coefficient of 0.7 between stainless steel hinges 114 a-b and plastic housings 120 a-b. Axis 104 with a diameter of 0.7 mm is nominally designed to pass through the center-of-mass of actuated sub-assembly 106. However due to mechanical tolerances during assembly, axis 104 may shift by up to 20 micrometers (μm), which will cause a gravity torque of up to 0.0001N-mm. Typical handshakes are up to 2 Hz and 0.1 degrees, causing angular accelerations of up to 0.3 rad/sec², and moment of inertia-provided torques are typically limited to 0.0003 N-mm. Thus, both gravity and handshake torques will not overcome a friction torque (mass×friction coefficient×hinge radius) of 0.001225 N-mm after current turn off.

FIG. 2 shows actuator 100 as part of folded camera structure (FCS) or simply “folded camera” 200. In folded camera 200, actuator 100 is used to rotate OPFE (e.g. prism) 102. The operation (actuation) of actuator 100 in folded camera 200 creates an extended tele field of view (FOV_(T)), of the type described for example in U.S. provisional patent applications 62/272,367 and 62/361,150. A typical rotational actuation stroke of actuator 100 in this case may be in the range of ±5 to ±20 degrees of the original position of OPFE 102, with resolution of at least 8 and up to 100 distinguishable steps (possible OPFE positions). Camera 200 further includes a lens element 202, and an image sensor 204. Camera 200 may further include an actuation mechanism for focusing and\or auto-focus (AF) of lens element 202. This actuation mechanism is not shown in FIG. 2, but may be for example as described in U.S. Pat. No. 9,392,188.

FIG. 3 shows folded camera 200 a part of a dual-camera (or “dual-aperture camera”) 300. Dual-camera 300 also includes a standard “upright” camera 302. Camera 302 has a standard camera structure, known in the art, and includes a lens 304 and an image sensor 306. Camera 302 may also include other parts such as actuation mechanism for the lens, a mechanical shield, a chassis and other parts, all known in the art and not shown in FIG. 3. Dual-aperture cameras such as camera 300 and their operation and use are described in detail in, for example, international patent application PCT/IB2016/056060.

Magnetic sensing element 126 is for example (as mentioned above) a Hall bar element, capable of measuring magnetic field in the X direction indicated in FIG. 1. In actuator 100, magnet 110 is rigidly coupled to (or is part of) actuated sub-assembly 116, while sensing element 126 is rigidly coupled to (or is part of) stationary sub-assembly 122. Magnet 110 has for example a magnetic field direction along the Z axis, such that the North magnetic pole is on the positive Z direction and the South magnetic pole is in the negative Z direction.

FIG. 4 shows a simulation of the effect of the magnetic field in the X direction on sensing element 126 as function of actuated sub-assembly 116 (and magnet 110) rotating around axis 104. It is apparent that the magnetic field changes monotonically from a negative value of about −0.2 T at one end of the movement range to +0.2 T at the other end of the movement (rotation) range.

FIG. 5 shows a known art electrical circuit 500 which allows reading of the magnetic field by a Hall bar element 126. Hall bar element 126 has 4 connectors marked as Iin, Gnd, V+ and V−. A current typically in the range of 1-20 mA is driven in Iin and flows through Hall bar element 126 to the ground (GND). Hall bar element 126 has a typical resistance in the range of 200-3000 kΩ. In this example, consider a sensing element with resistance 1200 ohm and current Iin=2.5 mA, such that the voltage drop between Iin and Gnd is 3V and is marked as Vin=3V. For the case of 0 (zero) magnetic field B in the X direction Vp=Vm=Vin/2=1.5V. If a magnetic field exists in Hall bar element 126, a voltage drop will be created between Vp and Vm, marked as Vout=Vp−Vm, such that Vp=(Vin+Vout)/2 and Vm=(Vin−Vout)/2. The size of Vout is proportional to the magnetic field B on the sensing element, i.e. Vout=αB. For a constant current Iin=2.5 mA, α has a typical value in the range of 0.2-2 mV/mT. In this example, consider α=0.5 mV/mT, such that for the graph seen in FIG. 4B, Vout is in the range of −100 mV to 100 mV in the movement range.

Amplifier 502 is an operational amplifier (op-amp) with a 3V driving voltage. The details of operation of op-amp 502 are known in the art and described here briefly. Op-amp 502 has an amplification factor β in the range of 5-200. In this example, assume an amplification factor of β=15. The inputs of op-amp 502 are Vp and Vm. The output of op-amp 502 is Vp+β(Vp−Vm). Hence, the voltage output of op-amp 502 (Vamp) in this example is in the range of 0-3V. Vamp is sampled by an analog-to-digital converter (ADC) 504, with resolution in the range of 8-14 bits, in this example 12 bits. Namely, the range 0 to 3V is divided to 4096 levels. Thus, circuit 500 allows the measurement of the motion range of actuator 100 with 12 bit maximal resolution (or 8-16 bits in other cases). For a 20 degree scanning range, this allows approximately 0.005 degree resolution. This resolution is worse than required.

FIG. 6A illustrates in an isomeric view, and FIG. 6B illustrates in an exploded view an actuator 600 of a rotational VCM according to another exemplary embodiment disclosed herein. Actuator 600 allows an extended OPFE scanning range plus OIS abilities. Compared to actuator 100, actuator 600 has an accurate position sensing mechanism that allows accuracy of 1/200 degrees, as described below. Thus, the control circuitry of actuator 600 can remain operative while the OPFE is rotated to a desired portion without reducing image optical quality.

Actuator 600 is similar mechanically to actuator 100 and includes all elements as actuator 100 (which consequently are numbered with identical numbers). The difference between actuator 600 and actuator 100 is that actuator 600 further includes two ball bearings 602 a and 602 b, typically made of stainless steel. Ball bearings 602 a and 602 b are fixedly attached (e.g. glued) inside housings 120 a and 120 b respectively. Actuated sub-assembly 116 is positioned inside stationary sub-assembly 122 such that hinges 114 a and 114 b are positioned inside ball bearings 602 a and 602 b respectively. Hinges 114 a and 114 b and bearings 602 a and 602 b are all concentric and lie on axis 104. The mechanical structure described allows the rotation of actuated sub-assembly 116 and light-folding-element 102 around the X axis with very low friction. A typical low friction coefficient of ball bearing 602 a and 602 b may be in the range of 0.001-0.005.

FIG. 7 shows actuator 600 as part of a folded camera 700. In folded camera 700, actuator 600 is used to rotate a light folding element as described above with reference to camera 200. The actuation creates an extended zoom field of view (FOV) as mentioned above and in addition provides OIS as described for example in PCT/IB2016/052179. As also indicated above, the typical rotational actuation stroke of actuator 600 should be in the range of ±8 to ±18 degrees of the original position of the light folding element, with resolution of at least 0.002 degrees. Camera 700 may further include elements described with reference to camera 200 above.

FIG. 8 shows camera 700 a part of a dual-camera 800. The description and use of dual-camera 800 are similar to those in camera 300 and are therefore not repeated.

In actuator 600, the actuation mechanism is responsible for both an extended scanning range and OIS. Thus, a higher scanning resolution is required, relative to that in actuator 100. FIG. 9 shows an electrical circuit 900 which allows reading of the magnetic field by Hall bar sensing element 126 for the extended scanning, according to an exemplary embodiment disclosed herein. Circuit 900 extends circuit 500 by including, in addition to the elements of circuit 500, a digital-to-analog converter (DAC) 902 with resolution in the range of 8-14 bits, and in this example 12 bits. Namely, the range 0 to 3V is divided to 4096 levels, or less than 1 mV. DAC 902 provides a reference voltage for a second amplification step, as explained next. The analog output of DAC 902 is marked as Vdac. Circuit 900 further includes op-amp 904, operating under voltage of 3V and amplification γ in the range of 100-4000. Exemplary, op-amp 904 demonstrates amplification of γ=500. The inputs of op-amp 904 are Vamp and Vdac. The output of op-amp 904 is Vdac+γ (Vdac−Vamp). Vdac is set in the following manner: the tilt (rotation) target of actuator 600 is known (decided by the user). The target range φ is divided into S steps, S is an integer, S>γ, in this example S=3000 (0.2 degrees in this example). For a given tilt target, a value “s” marks the closest integer step in the range. For example, if the target is −5 degrees than s=750. The DAC output is set to Vin/2−Vrange/2+Vrange*s/S. This setting of DAC output can assure that when the position of the actuator is closer to the target than (p/S the output of op-amp 502, Vamp2 is in the range of 0-3V. Vamp2 is sampled by an ADC 906, with resolution in the range of 8-14 bits, and in this example 12 bits. Namely, the range 0 to 3V is divided to 4096 levels. Thus, circuit 900 allows the measurement of the motion range of actuator 100 with γ times precision more than circuit 500. For 20 degrees scanning range, with γ=500, this allows approximately 0.00001 degree (10 micro-degree) resolution.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present disclosure.

While this disclosure has been described in terms of certain embodiments and generally associated methods, alterations and permutations of the embodiments and methods will be apparent to those skilled in the art. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims. 

1-7. (canceled)
 8. A folded digital camera comprising: a) an optical path folding element (OPFE) for folding an optical path from an imaged object or scene toward a lens and an image sensor of the folded digital camera, the folded digital camera having a field of view (FOV); and b) an actuator for rotating the OPFE for optical image stabilization (OIS), wherein the rotation of the OPFE further enables adjustment of the FOV over an extended scanning range greater than ±8 degrees and wherein OIS is enabled over the extended scanning range with sufficient resolution.
 9. The folded digital camera of claim 8, wherein the sufficient resolution is at least 0.002 degrees.
 10. The folded digital camera of claim 8, wherein the sufficient resolution is at least 0.005 degrees.
 11. The folded digital camera of claim 8, wherein the extended scanning range is up to ±20 degrees around a rest position of the OPFE.
 12. The folded digital camera of claim 9, wherein the extended scanning range is up to ±20 degrees around a rest position of the OPFE.
 13. The folded digital camera of claim 10, wherein the extended scanning range is up to ±20 degrees around a rest position of the OPFE.
 14. The folded digital camera of claim 8, wherein the actuator includes a position sensor for sensing an OPFE position relative to a stationary base of the folded digital camera.
 15. The folded digital camera of claim 14, wherein the position sensor includes a Hall bar sensor.
 16. The folded digital camera of claim 8, wherein the actuator includes a rotational voice coil motor (VCM) for rotating the OPFE.
 17. The folded digital camera of claim 16, wherein the rotational VCM includes a coil and a magnet, wherein the magnet is mechanically coupled to the OPFE and wherein the coil is coupled to the stationary base.
 18. The folded digital camera of claim 9, wherein the actuator includes a position sensor for sensing an OPFE position relative to a stationary base of the folded digital camera.
 19. The folded digital camera of claim 18, wherein the position sensor includes a Hall bar sensor.
 20. The folded digital camera of claim 9, wherein the actuator includes a rotational voice coil motor (VCM) for rotating the OPFE.
 21. The folded digital camera of claim 20, wherein the rotational VCM includes a coil and a magnet, wherein the magnet is mechanically coupled to the OPFE and wherein the coil is coupled to the stationary base.
 22. The folded digital camera of claim 10, wherein the actuator includes a position sensor for sensing an OPFE position relative to a stationary base of the folded digital camera.
 23. The folded digital camera of claim 22, wherein the position sensor includes a Hall bar sensor.
 24. The folded digital camera of claim 10, wherein the actuator includes a rotational voice coil motor (VCM) for rotating the OPFE.
 25. The folded digital camera of claim 24, wherein the rotational VCM includes a coil and a magnet, wherein the magnet is mechanically coupled to the OPFE and wherein the coil is coupled to the stationary base.
 26. A method, comprising: a) providing a folded digital camera having an optical path folding element (OPFE) for folding an optical path from an imaged object or scene toward a lens and an image sensor of the folded digital camera, the folded digital camera having a field of view (FOV); and b) rotating the OPFE to enable optical image stabilization (OIS), wherein the rotation of the OPFE further enables adjustment of the FOV over an extended scanning range greater than ±8 degrees and wherein OIS is enabled over the extended scanning range with sufficient resolution.
 27. The method of claim 26, wherein the sufficient resolution is at least 0.002 degrees.
 28. The method of claim 26, wherein the extended scanning range is up to ±20 degrees around a rest position of the OPFE. 